Suspicious FileFix Execution Pattern

Status: experimental
Severity: high
Log source: product windows, category process_creation
Author: 0xFustang, Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects suspicious FileFix execution patterns where users are tricked into running malicious commands through browser file upload dialog manipulation. This attack typically begins when users visit malicious websites impersonating legitimate services or news platforms, which may display fake CAPTCHA challenges or direct instructions to open file explorer and paste clipboard content. The clipboard content usually contains commands that download and execute malware, such as information stealing tools.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1204.004` User Execution: Malicious Copy and Paste

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation
Security-Auditing	Event ID 4688	A new process has been created.

Rule body yaml

title: Suspicious FileFix Execution Pattern
id: b5b29e4e-31fa-4fdf-b058-296e7a1aa0c2
related:
    - id: 4fee3d51-8069-4a4c-a0f7-924fcaff2c70
      type: similar
    - id: 4be03877-d5b6-4520-85c9-a5911c0a656c
      type: obsolete
status: experimental
description: |
    Detects suspicious FileFix execution patterns where users are tricked into running malicious commands through browser file upload dialog manipulation.
    This attack typically begins when users visit malicious websites impersonating legitimate services or news platforms,
    which may display fake CAPTCHA challenges or direct instructions to open file explorer and paste clipboard content.
    The clipboard content usually contains commands that download and execute malware, such as information stealing tools.
references:
    - https://mrd0x.com/filefix-clickfix-alternative/
    - https://expel.com/blog/cache-smuggling-when-a-picture-isnt-a-thousand-words/ # phishing lure directly asking users to open file explorer and paste command
    - https://blog.checkpoint.com/research/filefix-the-new-social-engineering-attack-building-on-clickfix-tested-in-the-wild/
author: 0xFustang, Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-11-24
tags:
    - attack.execution
    - attack.t1204.004
logsource:
    category: process_creation
    product: windows
detection:
    selection_exec_parent:
        # This is case where phishing pages trick users to paste commands in browser file upload dialog
        ParentImage|endswith:
            - '\brave.exe'
            - '\chrome.exe'
            - '\firefox.exe'
            - '\msedge.exe'
        CommandLine|contains: '#'
    selection_cli_lolbin:
        CommandLine|contains:
            - '%comspec%'
            - 'bitsadmin'
            - 'certutil'
            - 'cmd'
            - 'cscript'
            - 'curl'
            - 'finger'
            - 'mshta'
            - 'powershell'
            - 'pwsh'
            - 'regsvr32'
            - 'rundll32'
            - 'schtasks'
            - 'wget'
            - 'wscript'
    selection_cli_captcha:
        CommandLine|contains:
            - 'account'
            - 'anti-bot'
            - 'botcheck'
            - 'captcha'
            - 'challenge'
            - 'confirmation'
            - 'fraud'
            - 'human'
            - 'identification'
            - 'identificator'
            - 'identity'
            - 'robot'
            - 'validation'
            - 'verification'
            - 'verify'
    condition: selection_exec_parent and 1 of selection_cli_*
falsepositives:
    - Legitimate use of PowerShell or other utilities launched from browser extensions or automation tools
level: high

Stages and Predicates

Stage 0: `condition`

selection_exec_parent and 1 of selection_cli_*

Stage 1: `selection_exec_parent`

selection_exec_parent:
    ParentImage|endswith:
        - '\brave.exe'
        - '\chrome.exe'
        - '\firefox.exe'
        - '\msedge.exe'
    CommandLine|contains: '#'

Stage 2: `selection_cli_lolbin`

selection_cli_lolbin:
    CommandLine|contains:
        - '%comspec%'
        - 'bitsadmin'
        - 'certutil'
        - 'cmd'
        - 'cscript'
        - 'curl'
        - 'finger'
        - 'mshta'
        - 'powershell'
        - 'pwsh'
        - 'regsvr32'
        - 'rundll32'
        - 'schtasks'
        - 'wget'
        - 'wscript'

Stage 3: `selection_cli_captcha`

selection_cli_captcha:
    CommandLine|contains:
        - 'account'
        - 'anti-bot'
        - 'botcheck'
        - 'captcha'
        - 'challenge'
        - 'confirmation'
        - 'fraud'
        - 'human'
        - 'identification'
        - 'identificator'
        - 'identity'
        - 'robot'
        - 'validation'
        - 'verification'
        - 'verify'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`#` corpus 3 (sigma 3) `%comspec%` corpus 6 (sigma 5, splunk 1) `account` corpus 2 (sigma 2) `anti-bot` corpus 2 (sigma 2) `bitsadmin` corpus 10 (sigma 10) `botcheck` corpus 2 (sigma 2) `captcha` corpus 2 (sigma 2) `certutil` corpus 12 (sigma 10, kusto 2) `challenge` corpus 2 (sigma 2) `cmd` corpus 8 (sigma 8) `confirmation` corpus 2 (sigma 2) `cscript` corpus 15 (sigma 15) `curl` corpus 17 (sigma 14, elastic 2, splunk 1) `finger` corpus 2 (sigma 2) `fraud` corpus 2 (sigma 2) `human` corpus 2 (sigma 2) `identification` corpus 2 (sigma 2) `identificator` corpus 2 (sigma 2) `identity` corpus 2 (sigma 2) `mshta` corpus 14 (sigma 14) `powershell` corpus 25 (sigma 24, chronicle 1) `pwsh` corpus 7 (sigma 7) `regsvr32` corpus 15 (sigma 15) `robot` corpus 2 (sigma 2) `rundll32` corpus 26 (sigma 23, chronicle 2, kusto 1) `schtasks` corpus 6 (sigma 5, kusto 1) `validation` corpus 2 (sigma 2) `verification` corpus 2 (sigma 2) `verify` corpus 2 (sigma 2) `wget` corpus 11 (sigma 8, elastic 1, splunk 1, kusto 1) `wscript` corpus 16 (sigma 16)
`ParentImage`	ends_with	`\brave.exe` corpus 2 (sigma 2) `\chrome.exe` corpus 5 (sigma 5) `\firefox.exe` corpus 4 (sigma 4) `\msedge.exe` corpus 4 (sigma 4)

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Suspicious FileFix Execution Pattern

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_exec_parent`

Stage 2: `selection_cli_lolbin`

Stage 3: `selection_cli_captcha`

Indicators

Keyboard shortcuts

Search operators

Suspicious FileFix Execution Pattern

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_exec_parent

Stage 2: selection_cli_lolbin

Stage 3: selection_cli_captcha

Indicators

Stage 0: `condition`

Stage 1: `selection_exec_parent`

Stage 2: `selection_cli_lolbin`

Stage 3: `selection_cli_captcha`